1. Field of the Invention
The present invention relates to a method of designing a reflective surface of a reflector in a vehicle lamp used in vehicles such as automobiles and the like.
2. Related Background Art
A vehicle lamp is comprised of a light source (light source bulb) located at a predetermined light source position, a reflector for reflecting light from the light source bulb to the direction of the optical axis, and a lens for transmitting reflected light from the reflector and projecting the light to the outside of the lamp.
In the vehicle lamp of this structure, a light distribution pattern of the light emerging from the lamp is mainly determined by the shape and positional relation of the reflective surface of the reflector to the light from the light source bulb. Namely, the light from the light source bulb, impinging upon the reflective surface of the reflector, is reflected at respective regions of the reflective surface in accordance with reflection conditions such as reflection directions and optical diffusion conditions determined by surface shapes in the respective regions, and is projected as the reflected light out of the lamp. Part of the reflection conditions such as the optical diffusion conditions and others of the reflected light are also determined by the lens transmitting the reflected light.
The known reflective surfaces of reflectors used in the vehicle lamps, such as headlamps, include those described in Japanese Patent Publication No. S45-7397 and Japanese Patent Application Laid-Open No. H06-267302. For example, in the headlamp described in Publication No. S45-7397, the surface shape of the reflective surface is generated in such a way that a cross-sectional profile along the major axis direction of the reflective surface is defined as a hyperbola and the reflective surface is determined by an enveloping surface enveloping paraboloids of revolution that have the same focus as the hyperbola and that are tangent to the hyperbola.
In the headlamp described in Application LaidOpen No. H06-267302, the basic surface shape of the reflective surface is defined by a paraboloid of revolution and the center axis of revolution is set perpendicular to the optical axis. Then the surface shape of the reflective surface is generated by rotating each region of the paraboloid of revolution at an angle of revolution, which increases with distance from the optical axis, about the center axis of revolution.
Concerning the light emerging from the vehicle lamps as described above, the resultant light distribution pattern is required to satisfy certain conditions as to the range of emergence of the reflected light from the reflector, optical intensity in each reflection direction, etc., according to types, uses, and locations in the vehicle of the respective lamps. For this requirement, it is generally difficult to implement a light distribution pattern required of each lamp, by the foregoing configurations wherein the surface shape of the reflective surface is the simple combination of the quadratic curves, such as parabolas and hyperbolas, and the paraboloids of revolution.
Namely, the vehicle lamps need to meet (1) the conditions from the aspect concerning the function, such as the aforementioned light distribution pattern or the like, and, in addition thereto, (2) the conditions from the aspect concerning the shape (shape constraints) and (3) the conditions from the aspect concerning the appearance (appearance constraints) because of their use in a mounted state on the vehicles such as automobiles and the like. Particularly, a variety of conditions are recently being imposed on the tendency toward fascinating car styling, and so on.
In the reflectors of the lamps applied to the vehicles, it is thus necessary to implement the shape of the reflective surface capable of yielding the required light distribution pattern while satisfying the constraints from the shape aspect and the appearance aspect imposed about the area, the depth, and so on. Under such circumstances, the reflective surfaces of the surface shapes employing the paraboloids of revolution, hyperbolas, etc. allowed only low degrees of freedom in designing of the reflective surfaces and it was difficult to produce a reflective surface so as to satisfy all the various conditions for the function, shape, and appearance as described above.
Even in the case of a reflective surface of a surface shape resulting from some modification (rotation, fine adjustment of each region, etc.) of such surface shape, controllability of the light distribution pattern with the modification is not satisfactory, because a correspondence is not always definite between the modification of the reflective surface shape and change of the light distribution pattern. For this reason, the efficiency of a designing work is lowered in designing of the reflective surface for implementing the required distribution pattern, so as to pose a problem of necessity for a long time for the designing of the reflective surface.
It is an object of the present invention, which has been accomplished in order to solve the above problems, to provide a method of designing a reflective surface of a reflector in a vehicle lamp with improved controllability of the light distribution pattern and with improved efficiency of the designing work.
In order to accomplish the above object, a reflective surface designing method according to the present invention is a method of designing a reflective surface of a reflector used in a vehicle lamp, which comprises a first base curve generating step of generating a first base curve on a first base plane including an optical axis passing a light source position where a light source is placed and becoming a direction into which light from the light source is reflected by the reflector, and a first base axis perpendicular to the optical axis; a second base curve generating step of generating a plurality of second base curves extending in a direction of a second base axis perpendicular to the first base plane, for the first base curve; and a surface shape generating step of generating a surface shape of the reflective surface, based on the first base curve and the plurality of second base curves, wherein the first base curve generating step comprises repeating a step of generating one partial curve and thereafter generating a subsequent partial curve so as to be connected to said partial curve, thereby generating one first base curve consisting of a plurality of partial curves connected to each other, and wherein each partial curve is generated based on a shape parameter according thereto.
According to the above-stated method of designing the reflective surface of the reflector in the vehicle lamp, the shape of the reflective surface is generated by generating as a frame of the shape of the reflective surface the single first base curve (XY curve) on the first base plane (XY plane, e.g., a horizontal plane) including the optical axis (X-axis) and the first base axis (Y-axis) and the plurality of second base curves (XZ curves) extending nearly in the direction of the second base axis (Z-axis) from the points on the first base curve, and then spreading a curved surface based on them. The efficiency of the designing work is improved by applying the first base curve and the plurality of second base curves forming the frame, to the designing of the reflective surface.
Since one first base curve is formed by generating each partial curve, based on a shape parameter according to an area thereof and sequentially connecting such partial curves to each other, the controllability of the light distribution pattern is improved, as compared with a method using one shape parameter for the entire first base curve. Further, since the partial curves are sequentially generated from one side, the shape and light distribution pattern become smooth.
The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus are not to be considered as limiting the present invention.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.